A battery pack typically includes multiple rechargeable battery cells that are connected in series or parallel to store and supply electric power to a distribution system. Each battery cell includes a plurality of electrode foils having alternately-placed positive and negative charge portions. The electrode foils are separated by separator material and enclosed within a sealed outer pouch that is filled with an electrolyte solution. The separator material, e.g., polyethylene and/or polypropylene film, helps prevent an electrical short condition while permitting the free transfer of electrical charge between electrode foils.
Positive and negative terminals each extend a short distance outside of the sealed pouch for each battery cell. The positive charge portions of the electrode foils are ultrasonically welded together and welded to the positive terminal, and the negative charge portions of the electrode foils are ultrasonically welded together and welded to the negative terminal. The ultrasonic welds are internal to and contained within the sealed outer pouch. Process capability of the ultrasonic welding process that forms the internal weld may be subject to variation due to ultrasonic welder variations and other factors.